Exact model and OSX version is helpful information for offering suggestions.
"I went to DU and no hard drive is there" indicates you booted from the Recovery Disk or another drive.
Drive Utility will show the device (hard drive) and usually a partition on the device, usually.
Some have hard drives, some SSD.
Some have known problems with the hard drive cable.
El Capitan has a neutered version of Disk Utility

A Mac can be booted in Target Disk Mode (T key down at powerup) a firewire or thunderbolt icon floats onscreen.
If the Macbook is connected to another Mac with a firewire or thunderbolt cable, it's internal drives appear on the desktop. Unless the drive has failed electronically or mechanically.
IF the other Mac is started in Target Disk Mode, and connected, it's boot drives will appear in Boot Options (OPTION key down at powerup).

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